Voltage regulator arrangement for preventing overvoltages

ABSTRACT

Two closely coupled output windings of an AC generator have a common point. A first and second thyristor are connected across the windings, the voltages across each having opposite polarity. When the load voltage drops below a predetermined value, control pulses are applied to the gates of both thyristors. Therefore, they fire in turn, causing a substantially uninterrupted short circuit across both windings because of the close magnetic coupling between the windings.

Inventors Peter Ptelter Lauflen; Edgar Kuhn, Gerlingen, both of GermanyAppl. No. 38,378 Filed May 18, 1970 Patented Dec. 7, 1971 AssigneeRobert Bosch GmbH Stuttgart, Germany Priority May 23, 1969 Germany P 1926 317.3

VOLTAGE REGULATOR ARRANGEMENT FOR PREVENTING OVERVOLTAGES [56]References Cited UNITED STATES PATENTS 3,456,182 7/1969 Cummins et al.320/7l X 3,530,366 9/1970 Schwarm 322/28 Primary Examiner-T. E. LynchAssistant Examiner-J1. Huberfeld Attorney-Michael S. Striker ABSTRACT:Two closely coupled output windings of an AC generator have a commonpoint. A first and second thyristor are connected across the windings,the voltages across each having opposite polarity. When the load voltagedrops below a predetermined value, control pulses are applied to thegates of both thyristors. Therefore, they fire in turn, causing asubstantially uninterrupted short circuit across both windings becauseof the close magnetic coupling between the windings.

9 Claims, 1 Drawing Fig.

U.S. Cl 322/28, 322/90, 322/91, 322/93 Int. Cl H02p 9/00 Field of Search322/28, 89, 90,91, 93; 320/71 PATENIEUDEB Inn Edgar KUHN By theirATTORNEY INV ENTOR S PelerPFEFFER VOLTAGE REGULATOR ARRANGEMENT FORPREVENTING OVERVOLTAGES BACKGROUND OF THE INVENTION This inventionrelates to a voltage regulator for regulating the voltage across adirect current load when the voltage source is an alternating currentgenerator whose output is rectified. In particular; it relates to such aregulator wherein said alternating current generator has an outputwinding winding and wherein switching means are connected in parallel tosaid output winding, said switching means being controlled in such amanner that they become conductive when the voltage across the directcurrent load exceeds a predetermined voltage.

In particular, this invention relates to such a voltage regulator whenused in conjunction with a permanent magnet type of alternating currentgenerator. in known voltage regulator arrangements of this type, theseries combination of a transistor, a resistance and a diode isconnected in parallel with one output winding of the permanent magnetgenerator when the load voltage exceeds a predetermined voltage. In thismanner, the alternating voltage at this output winding is reduced onlyover one-half wave, but not over the other half wave. Thus duringoperation, high voltage peaks can appear across the direct current loadwhen no battery is connected in circuit. For a generator having al2-volt nominal voltage, these voltage peaks may reach over 200 voltsand are therefore very dangerous, particularly since in such nominallylow voltage arrangements, no such high voltages are expected.

However, it has been shown that particularly in the area in which suchpermanent magnet generators are used, namely in simple equipment as forexample construction machines, motorcycles, snow scooters, etc., itoften happens that the battery is removed for a period of time, forexample to start another engine. Thus accidents can resultif theoperator, after having removed the battery, touches thebattery-connecting cables, since these cables as mentioned above canreach dangerously high voltages when the known-type voltage regulatorarrangements are used.

SUMMARY OF TI-IE INVENTION lt is an object of the present invention tolimit the output,

voltages across a direct current load, in an arrangement as describedabove, so that these voltages are limited even when the battery isremoved.

This invention comprises a voltage regulator arrangement for regulatingthe load voltage across a direct current load. It comprises alternatingcurrent generating means having a first output winding and a secondoutput winding magnetically coupled to said first output winding.Rectifier means are connected to said first and second output windingsand furnish said load voltage between a first and a second rectifieroutput terminal. First switching means having a first control electrodeand adapted to have a unidirectional conducting state in response to acontrol signal applied to said first control electrode, and secondswitching rneans-having a second control electrode and adapted to have aunidirectional conducting state in response to a control signal appliedto said-second electrode are also furnished. Connecting means connectsaid first switching means across said first output winding andsaidsecond switching means across said second output winding in such amanner that a substantially continuous short circuit exists across saidmagnetically coupled output windings in response to control signals atsaid first and second control electrodes. Finally, control circuit meansconnected between said direct current load and said control electrodesfurnish said control signals in dependence upon said load voltage.

The substantially uninterrupted circuit is obtained by using asswitching means a first and second thyristor and by controlling saidthyristors in such a manner that one short circuits the positive halfwave, while the other short circuits the negative half wave. Because ofthe magnetic coupling between the windings short circuiting one of thewindings, results in a short transistor at the output. First and secondvoltage divider means, each having a voltage divider tap, may beconnected to the emitter-collector circuit of said transistor. By suchan arrangement, connecting the control electrodes of the thyristors tosaid voltage divider taps results in substantially equal currentdistribution for the ignition of each'of the two thyristors. Thesafety-of the arrangement may be increased even more, if an additionalcontrol element having a predetermined voltage breakdown characteristic,as for example a Zener diode, is connected in parallel with theemitter-collector circuit of said switching control transistor. In thiscase, any increase in load voltage over a predetermined voltage valuecauses this element to become conductive again causing ignition of thethyristors via the first and second voltage divider means whichinterconnect the gates of the thyristors and the emitter-collectorcircuit of the switching transistors.

If the output voltage increases very rapidly, for example because thebattery has been removed, the Zener diode breakdown causes the thyristorto become activated almost instantaneously, thus limiting the outputvoltage before this can reach a dangerous value. This arrangement hasproven itself greatly in practice, since here the voltages can belimited to a value which will in most cases produce no danger to theoperator.

In A particularly simple embodiment of the present invention, asingle-phase alternating current generator has first and second outputwindings which are connected at a common point. Parallel to each ofthese output windings is a thyristor, each of the thyristors having thecorresponding electrode, for example both anodes, connected to saidcommon point. Here a particularly simple connection to the controlelectrodes of the thyristors results and no pulse transformer isrequired.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, bothas to its construction and its method ofoperation, together. with additional objects and advantages thereof,will be best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a schematiccircuit diagram of a control arrangement, in accordance with thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The single FIGURE shows apermanent magnet singlephase alternating current generator 11, utilizingpermanent magnet 10. The alternating current generator has a first andsecond winding, 14 and 15 connected at a common point 13. This commonpoint 13 is connected to ground, while the free end of windings l4 and15 is connected, respectively, to the anode of a diode '16 and 17.Cathodes of diodes l6 and 17 are connected in common to the positivevoltage line 18 connected to the positive terminal 22 of a battery whichconstitutes a part of the direct current load circuit. The otherterminal of the battery is connected to ground. The battery may,

for example. be a l2-volt battery. A direct current load 23, for examplea headlight, an ignition-circuit. etc., can be connected betweenpositive line 18 and ground by means of a switch 24. It is obvious thatthe output windings I4 and 15 which are magnetically closely coupled toeach other via the magnetic circuit of generator 11, constitute asingle-phase center tap rectifier circuit when used in conjunction withdiodes l6 and 17.

The voltage regulator circuit is denoted by 26. It comprises first andsecond switching means, in this embodiment thyristors 32 and 33,respectively, and. control circuit means which are embodied in theremainder of block 26, excluding said thyristors.

Specifically, the control circuit means comprise a control switchingtransistor 28 which is operated as a switch and furnishes enough currentfor full ignition to thyristors 32 and 33 when in the conductive state.Transistor 28 is driven by a transistor 27 in such a manner thattransistor 28 is switched on," i.e. to the conductive state, when theload voltage exceeds a predetermined load voltage.

The voltage regulator circuit 26 is constructed as follows: The cathodesof thyristors 32 and 33 are connected to ground. The anode of thyristor32 is connected to the anode of diode 16 and the free end of winding 14,while the anode of thyristor 33, in common with the anode of diode 17,is connected to the free end of output winding 15. The gates ofthyristors 32 and 33 are, respectively, connected to ground via aresistance 34 and 35, for example l,000 ohms each. and to a circuitpoint 38, the control circuit output terminal, via a resistor 36 and 37,for example 400 ohms. The collector of transistor 28 is also connectedto the control circuit output terminal, namely terminal 38, while itsemitter is connected to line 18. Connected in parallel with theemitter-collector circuit of transistor 28 is an additional controlelement, namely a Zener diode 39. Specifically, the anode of Zener diode39 is connected to point 38.

The base of transistor 28 is connected to line 18 via a resistor 42 andto the collector of transistor 27 via a resistor 43. The emitter oftransistor 27, an NPN-transistor, is directly connected to the cathodeof a Zener diode 44 whose anode is connected to ground. It is furtherconnected to line 18 via a resistor 45, for example 4 H2. The anode ofZener diode 44 is connected to ground, so that emitter of transistor 27has a relatively constant potential relative to ground when the circuitis in operation. This voltage may, for example, be 8 volts. Thirdvoltage divider means comprising a resistor 48 and 49 are connected fromline 18 to ground. The common point of resistors 48 and 49 is called thecontrol circuit input. The control circuit input is connected to thebase of transistor 27 via a temperature compensating diode 46 whoseanode is connected to the control circuit input, point 47, while itscathode is connected to the base of transistor 27. A capacitor 50 of,for example, 1.5 microthodes, is connected between point 47 and ground.Further, a resistor 53, positive feedback means, is connected betweenthe collector of transistor 28 and point 47. Use of this resistor causestransistor 28 to act as a switch, that is, the transistor is eitherfully conductive or fully blocked, as will be described below.

OPERATION In operation, generator 11 is driven by suitable drivingmeans, for example by the engine of a snow scooter, that is it is drivenwith a variable speed. The load, too, is variable, for example itdepends upon whether battery 22 is fully charged or fully discharged,and whether a load 23 is or is not in the circuit. Voltages are inducedin output windings 14 and 15 which are rectified by diodes 16 an 17 andapplied to battery 22 and, if it is in the circuit, load 23. Thus thevoltage at battery 22 and thus the voltage between lines 18 and 19 willincrease.

This increase in voltage results in a corresponding increase in thevoltage between point 47 and ground. As long as this voltage is underapproximately 9 volts, transistor 27 is blocked and in turn, blockstransistor 28 by blocking its base current. Therefore, the controlelectrodes of thyristors 32 and 33 also receive no current causing thesethyristors to be blocked.

If the voltage between point 47 and ground rises above 9 volts, a basecurrent flows in transistor 27 and this becomes conductive. Thus, thebase current for transistor 28 can flow over the collector-emittercircuit of transistor 27 and transistor 28 also becomes conductive. Thiscauses the voltage at the collector of transistor 28, namely the voltageat the control circuit output terminal to increase. This change inpotential again results in an increase at point 47 causing transistor 27to become fully conductive. thus causing transistor 28 to become fullyconductive also. This circuit operation takes place within a very shorttime. When transistor 28 is fully conductive, a control current isapplied to the gates of thyristors 32 and 33 so that thyristor becomesconductive whose anode is, at that moment, positive with respect to itscathode. By arranging the interconnecting means between point 38 and thecontrol electrodes to be two parallel paths comprising identicalresistors, the control current for each of the thyristors will besubstantially equal to the control current of the other, for example 30milliampheres each.

If it is assumed that at first a positive voltage exists acrossthyristor 32, this thyristor becomes conductive and directly shortcircuits winding 14. Because of the close magnetic coupling betweenwindings 14 and 15, this short circuit essentially short circuitswinding 15 also.

If, after a half period of the applied voltage, the anode of thyristor32 becomes negative and that of thyristor 33 becomes positive, the shortcircuit current is transferred to thyristor 33 so that this thyristordirectly short circuits winding 15 and, because of the magneticcoupling, also short circuits winding 14. As long as transistor 28remains conductive, both output windings of the alternating currentgenerator, namely windings l4 and 15, are short circuited substantiallywithout interruption so that only a voltage of approximately 1 volt isdeveloped across them and no current is allowed to flow to the DC loadcircuit connected to lines 18 and 19. Diodes l6 and 17 prevent a shortcircuiting of the battery over thyristors 32 and 33. Since the batteryis now no longer being charged, the voltage at its terminals willgradually decrease causing the base current of transistor 28 to bereduced and its collector potential to become negative. This change ofpotential is transferred to point 47 via resistor 53 so that transistor27 becomes fully blocked in turn blocking transistor 28. Thus thecurrent to the gates of thyristors 32 is blocked and the thyristors alsobecome blockedas soon as the voltage at the last conducting thyristorbecomes negative. Generator 11 then again furnishes current to battery22 via rectifiers l6 and 17 so that the voltage at the battery againrises and the above cycle repeats. During operation, transistor 28 maybe switched several hundred times a second, depending upon the operatingconditions of generator 11 with respect to speed and load.

In practice, battery 22 is often disconnected in small equipment inorder that other equipment may be started. When the battery is removed,the voltage at the battery terminals can rise very rapidly, especiallyif the generator is being driven at high speed. Voltage peaks may reacha high of 200 volts. This voltage not only endangers the semiconductorelements in the regulating circuit, but also present a danger for theoperator who removes and replaces the battery. In particular, asmentioned above, this voltage presents a danger because the operatordoes not expect such a high voltage. When the voltage changes occur varyrapidly, the above-described regulating arrangement cannot immediatelylimit the output voltage since a determined time delay is introduced bycapacitor 50.

Use of the Zener diode 39 results in a safe limitation of voltage evenunder these conditions. As soon as the voltage between lines 18 and 19exceeds a value as for example 25 volts, Zener diode 39 becomesconductive so that a control current flows to thyristors 32 and 33causing that thyristor to become conductive whose anode is at thatmoment positive. Since the thyristors switch with extremely short timedelay, it is possible to limit the voltage between lines 18 and 19 to asafe value substantially instantaneously.

it is obvious that the illustrated construction of the circuit isparticularly simple. This is achieved in part by the fact thattransistors 27 and 28 are of opposite types, that is, one is anNPN-transistor while the other is a PNP-transistor. It is furtherachieved by the control circuit used for thyristors 32 and 33, namelythe first and second voltage dividers and also by the good use made ofthe close magnetic coupling between output windings l4 and 15 ofgenerator 11. Even the common connection of the cathodes of boththyristors to ground, leads to a particularly simple circuit. Because ofthe mode of operation of the switching transistor, thyristors 32 and 33are always either fully conductive or totally blocked, that is, thesethyristors are operated under optimal conditions.

While the invention has been illustrated and described as embodied inparticular types of switching elements and a particular type of controlmeans, it is not intended to be limited to the details shown, sincevarious modifications and circuit changes may be made without departingin any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. Voltage regulator arrangement for regulating the load voltage acrossa direct current load, comprising, in combination, alternating currentgenerating means having a first output winding, and a second outputwinding magnetically coupled to said first output winding; rectifiermeans interconnecting said first and second output windings and saiddirect current load; first and second switching means, having a firstand second control electrode respectively and adapted to have aunidirectional conducting state in response to control signals appliedto said control electrodes; means connecting said first switching meansacross said first output winding; means connecting said switching meansacross said second output winding in such a manner that a substantiallycontinuous short circuit exists across said magnetically coupled outputwindings in response to control signals at said first and second controlelectrodes; and control circuit means connected between said directcurrent load and said control electrodes, said control circuit meanscomprising: a control circuit output terminal; control switchingtransistor means having an emitter-collector circuit interconnectedbetween one side of said direct current load and said control circuitoutput terminal for changing the voltage at said control circuit outputterminal from a first to a second level when said load voltage exceeds apredetermined voltage; interconnecting means interconnecting saidcontrol circuit output terminal and said first and second controlelectrode in such a manner that said second level constitutes said firstand second control signals; and an additional control element having apredetermined voltage breakdown characteristic connected in parallelwith said emitter-collector circuit of said control switchingtransistor.

2. A voltage regulator arrangement as set forth in claim 1, wherein saidalternating current generating means comprise a pennanent magnetgenerator.

3. A voltage regulator arrangement as set forth in claim 2, wherein saidfirst and second switching means respectively comprise a first andsecond thyristor.

4. A voltage regulator arrangement as set forth in claim l, wherein saidcontrol switching transistor has a base; and wherein said controlcircuit means further comprise an amplifier transistor having anamplifier transistor output circuit connected to said base of saidswitching transistor and an am plifier transistor input circuit; furthercomprising positive feedback means connected between said controlcircuit output terminal and said amplifier transistor input circuit.

5. A voltage regulator arrangement as set forth in claim 4, wherein saidpositive feedback means comprise a resistor.

6. A voltage regulator arrangement as set forth in claim 5, wherein saidcontrol switching transistor is a PNP-transistor; and wherein saidamplifier transistor is an NPN-transistor.

7. A voltage regulator arrangement as set forth in claim 6, wherein saidalternating current generating means comprise a single-phase generator;wherein said single-phase generator has a first and second outputwinding connected at a common point; wherein said first and secondthyristors are connected, respectively, across said first and secondoutput winding, corresponding electrodes of said thyristors beingconnected to said common point.

8. A voltage regulator arrangement as set forth In claim 1,

wherein said additional control element comprises Zener diode.

9. A voltage regulator arrangement as set forth in claim 1, wherein saidinterconnecting means interconnecting said control circuit outputterminal and said first and second control electrodes comprise first andsecond voltage divider means having, respectively, a first and secondvoltage tap respectively connected to said first and second controlelectrodes.

1. Voltage regulator arrangement for regulating the load voltage acrossa direct current load, comprising, in combination, alternating currentgenerating means having a first output winding, and a second outputwinding magnetically coupled to said first output winding; rectifiermeans interconnecting said first and second output windings and saiddirect current load; first and second switching means, having a firstand second control electrode respectively and adapted to have aunidirectional conducting state in response to control signals appliedto said control electrodes; means connecting said first switching meansacross said first output winding; means connecting said switching meansacross said second output winding in such a manner that a substantiallycontinuous short circuit exists across said magnetically coupled outputwindings in response to control signals at said first and second controlelectrodes; and control circuit means connected between said directcurrent load and said control electrodes, said control circuit meanscomprising: a control circuit Output terminal; control switchingtransistor means having an emitter-collector circuit interconnectedbetween one side of said direct current load and said control circuitoutput terminal for changing the voltage at said control circuit outputterminal from a first to a second level when said load voltage exceeds apredetermined voltage; interconnecting means interconnecting saidcontrol circuit output terminal and said first and second controlelectrode in such a manner that said second level constitutes said firstand second control signals; and an additional control element having apredetermined voltage breakdown characteristic connected in parallelwith said emittercollector circuit of said control switching transistor.2. A voltage regulator arrangement as set forth in claim 1, wherein saidalternating current generating means comprise a permanent magnetgenerator.
 3. A voltage regulator arrangement as set forth in claim 2,wherein said first and second switching means respectively comprise afirst and second thyristor.
 4. A voltage regulator arrangement as setforth in claim 1, wherein said control switching transistor has a base;and wherein said control circuit means further comprise an amplifiertransistor having an amplifier transistor output circuit connected tosaid base of said switching transistor and an amplifier transistor inputcircuit; further comprising positive feedback means connected betweensaid control circuit output terminal and said amplifier transistor inputcircuit.
 5. A voltage regulator arrangement as set forth in claim 4,wherein said positive feedback means comprise a resistor.
 6. A voltageregulator arrangement as set forth in claim 5, wherein said controlswitching transistor is a PNP-transistor; and wherein said amplifiertransistor is an NPN-transistor.
 7. A voltage regulator arrangement asset forth in claim 6, wherein said alternating current generating meanscomprise a single-phase generator; wherein said single-phase generatorhas a first and second output winding connected at a common point;wherein said first and second thyristors are connected, respectively,across said first and second output winding, corresponding electrodes ofsaid thyristors being connected to said common point.
 8. A voltageregulator arrangement as set forth in claim 1, wherein said additionalcontrol element comprises Zener diode.
 9. A voltage regulatorarrangement as set forth in claim 1, wherein said interconnecting meansinterconnecting said control circuit output terminal and said first andsecond control electrodes comprise first and second voltage dividermeans having, respectively, a first and second voltage tap respectivelyconnected to said first and second control electrodes.